Western Great Lakes Bird & Bat Observatory

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MEET ONE OF FBMP’S NEW SPECIES: BELL'S VIREO

 By Kate Redmond

It’s a small (just under five inches long), drab bird, not particularly noisy, easy to overlook, and it certainly wasn’t supposed to be at Forest Beach. People routinely travel to the Wisconsin River Valley or the far southwestern corner of Wisconsin to add it to their state list, and it’s at the edge of its range there. But in June, WGLBBO Director Bill Mueller heard its distinctive cheedle-cheedle-cheedle song, and then he saw it – a Bell’s Vireo, the 254th species listed for the Forest Beach Migratory Preserve property.

Bell’s Vireos (Vireo bellii) breed in the Central Plains and the Southwest, south into northern Mexico, and the majority spend the winter along Mexico’s Pacific coast. They‘re found in dense, brushy areas within woodlands and grasslands and along stream edges. One of 13 species of vireos in the U.S., Bell’s Vireo has been holding steady over the middle of its range but declining in California and in the Midwest; it is considered a Threatened species in Wisconsin and Endangered in other areas.  

Habitat loss, habitat alteration due to invasive shrubs, and Brown-headed Cowbirds are the main reasons for its decline. Cowbirds locate the nests, lay their eggs among the vireo eggs, and move on, leaving the vireos to rear both clutches. It’s a child-rearing strategy that served the cowbirds well when they followed giant, migratory herds of bison around the Great Plains, eating insects kicked up by uncountable hooves. Alas for the young vireos, the larger cowbird nestlings claim most of the food and eventually elbow them out of the nest.  

Like other vireos, Bell’s Vireos eat insects on their summer range (they haven’t been studied much on their winter range), but they are unusual because their diet includes some fairly big prey for the bird’s size. They forage, often in pairs, in the leaves of shrubs and trees and occasionally fly out to hawk insects from the air. Stinkbugs, bees, wasps, grasshoppers, and a variety of beetles and caterpillars are fair game, as are spiders. According to several sources, no one has ever seen a Bell’s Vireo drink water. Apparently, they get all the liquid they need from their food.

They build their nests two to five feet above the ground, hanging in the fork of a horizontal twig. Cornell University’s All About Birds site describes the nest as an “Open bag-like or basket-like cup of grass, straw-like stems, plant fibers, small skeletonized leaves, paper, and strips of bark fastened with spider silk; lined almost invariably with fine, brown or yellow grass stems. Outside decorated with spider egg cases.” 

The eggs (usually four) hatch in about two weeks, and although the young fledge in about 12 days, their parents continue to feed them for another three weeks. Both parents share (though not evenly) in nest-building, incubation, and feeding the young. Adults may return to the same territory the following year; the oldest known Bell’s Vireo was recaptured eight years after being banded.

Who put the Bell in Bell’s Vireo? John James Audubon himself. He named the bird after collector and taxidermist John Graham Bell, who accompanied Audubon on a trip on the Missouri River.